1. Field of the Invention
This invention relates to oil and gas drilling, and more particularly to apparatus and methods for reliably transmitting information between downhole drilling components.
2. Background of the Invention
In the downhole drilling industry, MWD and LWD tools are used to take measurements and gather information concerning downhole geological formations, status of downhole tools, and other conditions located downhole. Such data is useful to drill operators, geologists, engineers, and other personnel located at the surface. This data may be used to adjust drilling parameters, such as drilling direction, penetration speed, and the like, to effectively tap into an oil or gas bearing reservoir. Data may be gathered at various points along the drill string, such as from a bottom hole assembly or from sensors distributed along the drill string.
Nevertheless, data gathering and analysis represent only certain aspects of the overall process. Once gathered, apparatus and methods are needed to rapidly and reliably transmit the data to the earth's surface. Traditionally, technologies such as mud pulse telemetry have been used to transmit data to the surface. However, most traditional methods are limited to very slow data rates and are inadequate for transmitting large quantities of data at high speeds.
In order to overcome these limitations, various efforts have been made to transmit data along electrical and other types of cable integrated directly into drill string components, such as sections of drill pipe. In such systems, electrical contacts or other transmission elements are used to transmit data across tool joints or connection points in the drill string. Nevertheless, many of these efforts have been largely abandoned or frustrated due to unreliability and complexity.
For example, drill strings may include hundreds of sections of drill pipe and other downhole tools connected in series. In order to reach the surface, data must be transmitted reliably across each tool joint. A single faulty connection may break the link between downhole sensors and the surface. Also, because of the inherent linear structure of a drill string, it is very difficult to build redundancy into the system.
The unreliability of various known contact systems is due to several factors. First, since the tool joints are typically screwed together, each of the tools rotate with respect to one another. This causes the contacts to rotate with respect to one another, causing wear, damage, and possible misalignment. In addition, as the tool joints are threaded together, mating surfaces of the downhole tools, such as the primary and secondary shoulders, come into contact. Since downhole tools are not typically manufactured with precise tolerances that may be required by electrical contacts, this may cause inconsistent contact between the contacts.
Moreover, the treatment and handling of drill string components is often harsh. For example, as sections of drill pipe or other tools are connected together, ends of the drill pipe may strike or contact other objects. Thus, delicate contacts or transmission elements located at the tool ends can be easily damaged. In addition, substances such as drilling fluids, mud, sand, dirt, rocks, lubricants, or other substances may be present at or between the tool joints. This may degrade connectivity at the tools joints. Moreover, the transmission elements may be subjected to these conditions each time downhole tools are connected and disconnected.
Thus, what are needed are reliable contacts for transmitting data across tool joints that are capable of overcoming the previously mentioned challenges.
What are further needed are reliable contacts that are resistant to wear and tear encountered in a downhole environment.
What are further needed are reliable contacts that, even when damaged, still provide reliable connectivity.
What are further needed are apparatus and method to adjust the impedance of the contacts to minimize signal reflections at the tool joints.